Firmware update not being applied?

I have a RT-AC68U and running an old version of the merlin firmware (3.0.0.4.374.43_2). It has been working perfectly, so haven't kept up with the recent updates. I decided to download the current firmware (RT-AC68U_380.68_2.zip). I extracted the RT-AC68U_380.68_2.trx file, and select it under "Administration / Firmware Upgrade / Upload". It is showing that it is working for 3 minutes, and then at the end I come back to the exact same version I started with, and not the new version. Is it too big of a step in versions? If so, how do I switch to the latest version?